Recently, environmentally friendly vehicles including an electric vehicle, a fuel cell vehicle and a hybrid vehicle using both motor and engine have attracting attention. Mounting a plurality of batteries on such a vehicle that has a power source device mounted thereon has also been proposed.
In designing such a vehicle, a method of charging the plurality of batteries must also be considered. Various proposals have been made in relation to the method of charging a plurality of batteries.
By way of example, Japanese Patent Laying-Open No. 9-233710 discloses a charge/discharge device capable of individually charging and discharging a plurality of storage batteries. The charge/discharge device includes a charge rectifying circuit for rectifying an AC power source, a regeneration rectifying circuit connected anti-parallel to the charge rectifying circuit, for regenerating electricity of the storage batteries divided into a plurality of numbers to the AC power source, and a plurality of step-up/down converters provided corresponding to the plurality of storage batteries, respectively. Each of the plurality of step-up/down converters is used as a step-down converter when the storage battery is charged, and used as a step-up converter when the storage battery is discharged.
In the charge/discharge device described in Japanese Patent Laying-Open No. 9-233710, charging of a storage battery is difficult unless the output voltage of the charge rectifying circuit is made higher than the voltage across terminals of the storage battery. In order to solve this problem, it is necessary to use a power source device capable of outputting a high voltage, or to provide a voltage boosting circuit between the AC power source and the charge rectifying circuit.
When a plurality of storage batteries mounted on a vehicle are to be charged using the technique described in the laid-open application mentioned above, it may be possible to use a high-voltage power source or to connect a boosting circuit between a commercial power source for home use and the storage battery. According to these methods, however, a dedicated charging device, for example, becomes necessary. This undesirably increases the number of components of a vehicle. Further, an operation of connecting the charging device becomes necessary and, hence, increased burden on the user is expected.